This invention relates to a circuit arrangement for enhancing the transconductance of a differential amplifier stage comprising a pair of MOS transistors, having respective source electrodes connected together through a circuit node.
As is well known, the differential stage or cell is one of the most widely used circuit components to be employed in a comprehensive range of analog circuit designs.
The structure of a bipolar technology differential stage comprises a pair of transistors which are connected together by way of their respective emitters through a circuit node which is also connected to a negative supply pole via a bias current source.
Also known are differential stages using the MOS technology, that is comprising a pair of field-effect transistors of the MOS type which have respective source electrodes connected together through the aforesaid circuit node.
Structures of the above-mentioned kind are described, for instance, in the publication: "Analysis and Design of Analog Integrated Circuits", Wiley & Sons, 1986.
It is a recognized fact that the electric signal input to a differential stage is represented by a voltage value Vin equal to the difference of the voltage values applied to the respective bases of the transistor pair, or to the respective gates of the MOS transistor pair.
The output electric signal is represented instead by a current Iout given by the difference between the values of the currents flowing through the respective collectors of the bipolar transistor pair, or the respective drains of the MOS transistor pair.